Abrasive material having an antiloading coating

ABSTRACT

To determine what fine structure of the surface on which antiloading agents are applied performs the function of antiloading agents sufficiently. An abrasive material having an antiloading coating on an outermost surface thereof, in which the antiloading coating contains an antiloading agent and a binding resin, the binding resin is formed into a film with cracks, and a reticulate fine structure is formed on an entire surface of the antiloading coating by the cracks.

CROSS-REFERENCE TO PRIORITY APPLICATION

This application claims priority from Japanese patent application SerialNo. 2004-203510, filed Jul. 9, 2004.

BACKGROUND

The present invention relates to an abrasive material having anantiloading coating on an outermost surface thereof, and particularly anabrasive material having an antiloading coating whose entire surface isreticulately cracked.

SUMMARY

In an abrasive material obtained by applying a multitude of abrasiveparticles together with binding resin, there is some degree of spacebetween the abrasive particles. During the abrading process, materialabraded from a body to be abraded, also known as swarf, tends to fillspaces between abrasive particles.

The filling of spaces between abrasive particles with swarf and thesubsequent build-up of swarf is known as loading. Loading causes aproblem because the function of abrasive particles is hindered and thecut rate of abrasive particles is decreased (thus, more force may berequired to abrade). In addition, loading is an exponential problem;once swarf begins to fill in spaces between abrasive particles, theinitial swarf acts as a “seed” or “nucleus” for additional loading.

The abrasive material industry has sought antiloading materials to usein as abrasives. Examples of antiloading materials which have been usedinclude metal salts of fatty acids, urea-formaldehyde resins, waxes,mineral oils, crosslinked silanes, crosslinked silicones, andfluorohydrocarbons.

For example, antiloading agents for abrasives have been known, whichcomprise metal salts of carboxylic acids having hydrocarbon chain,phosphates having hydrocarbon chain and ammonium having hydrocarbonchain, amines, imines and carboxylic acids having hydrocarbon chain, andacid anhydrides, and quaternary ammonium anti-static compounds. Theseantiloading agents are borne on an outermost surface of coated abrasivesso as to serve for the abrading work. The antiloading agents areoccasionally applied with a binder in order to assist in being retainedon the surface.

Also, in the case where an abrasive article has a size coat and asupersize coat on abrasive particles, antiloading agents areoccasionally contained therein.

In the case where antiloading agents are applied to abrasives, it hasbeen conventionally thought that the function of antiloading agents issufficiently performed by retaining the antiloading agents between anabrasive surface of abrasive materials and a body to be abraded. Thus,in the case where antiloading agents are applied on an abrasive surfaceor contained in an outermost resin layer, sufficient studies have notbeen made so far on a state in which the antiloading agents are retainedon the abrasive surface. Also, it has not been known what influence afine structure of the surface on which antiloading agents are appliedhas on abrasive performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electron micrograph showing a surface of an antiloadingcoating of an abrasive material in Example 1.

FIG. 2 is an electron micrograph showing a surface of an antiloadingcoating of an abrasive material in Example 1 after being used.

FIG. 3 is an electron micrograph showing a surface of an antiloadingcoating of an abrasive material in Example 2.

FIG. 4 is an electron micrograph showing a surface of an antiloadingcoating of an abrasive material in Example 2 after being used.

FIG. 5 is an electron micrograph showing a surface of an antiloadingcoating of an abrasive material in Comparative Example 1.

FIG. 6 is an electron micrograph showing a surface of an antiloadingcoating of an abrasive material in Comparative Example 1 after beingused.

FIG. 7 is an electron micrograph showing a surface of an antiloadingcoating of an abrasive material in Comparative Example 2.

FIG. 8 is an electron micrograph showing a surface of an antiloadingcoating of an abrasive material in Comparative Example 2 after beingused.

DETAILED DESCRIPTION

The present invention solves the above-mentioned conventional problem,and the object thereof is to determine what fine structure of thesurface on which antiloading agents are applied performs the function ofantiloading agents sufficiently.

The present invention provides an abrasive material having anantiloading coating on an outermost surface thereof, in which

-   -   the antiloading coating contains an antiloading agent and a        binding resin;    -   the binding resin is formed into a film with cracks; and    -   a reticulate fine structure is formed on an entire surface of        the antiloading coating by the cracks, whereby the        above-mentioned object is achieved.

An abrasive material of the present invention is preferably produced bya method comprising the steps of:

-   -   providing an abrasive material;    -   applying an antiloading agent composition containing an        antiloading agent and a binding resin on an outermost surface of        the abrasive material; and    -   forming the binding resin into a film with cracks by heating the        abrasive material to form a reticulate fine structure on an        entire surface of an antiloading coating by the cracks.

An abrasive material of the present invention has a superior capabilityof discharging swarf and a markedly improved cutting performance.

An abrasive material having an antiloading coating on an outermostsurface thereof of the present invention comprises an antiloading agentcomposition coated on an outermost surface of a generally known abrasivematerial. Kinds of abrasives on which an antiloading agent compositionis coated are not particularly limited and may be such that anantiloading agent has been conventionally used for the abrading work.Such abrasives include many kinds such as a bonded abrasive material, acoated abrasive material and a nonwoven abrasive material.

For example, a bonded abrasive material comprises a multitude ofabrasive particles fixed by a binding resin. A coated abrasive materialcomprises abrasive particles stuck to a substrate by a binding resin. Anonwoven abrasive material comprises abrasive particles stuck into oronto a three-dimensional nonwoven substrate by a binding resin. Eachtype of the abrasives may be in a variety of forms. For example, acoated abrasive material may comprise a first layer (also known as amake coat), a plurality of abrasive particles stuck to or into the firstlayer, and a second layer (also known as a size coat). In some cases, athird layer (also known as a supersize coat) may be applied onto thesize coat. In addition, a coated abrasive material can be of forms suchas a belt, a disk and a seat.

An outermost surface of an abrasive material denotes a surface of anabrasive material which will touch a body to be abraded in the case ofnot coating an antiloading agent composition thereon. That is, theoutermost surface signifies a surface on the size coat in the presenceof the make coat and the size coat, and meanwhile a surface on the makecoat and the abrasive particles in the presence of only the make coat.Also, the outermost surface denotes a surface of resin used for thebonding in the case of a nonwoven abrasive product and a bonded abrasiveproduct.

An antiloading agent composition denotes a coating solution containingan antiloading agent, a binding resin and a solvent. The antiloadingagent may be such as to be conventionally used; typically includingmetallic soap having the antiloading effect, particularly stearates suchas zinc stearate, calcium stearate and lithium stearate, metal salts offatty acids, waxes and graphite. An additive such as fluorohydrocarbonmay be used together.

A binding resin may be such as to be formed into a film with cracks, bywhich a reticulate fine structure can be formed on an entire surface ofthe coating. The cracks of the coating and the reticulate fine structurecan be generally formed by adjusting hardness of resin and film-formingconditions. The hardness of resin is adjusted by changing glasstransition temperature (Tg). The film-forming conditions are adjusted bychanging heating temperature and time. particulate resin dispersed intoa solvent is generally used for the binding resin. The solvent may be anaqueous solvent consisting essentially of water. The binding resin ispreferably in a form of an aqueous latex or an aqueous resin emulsion.

The binding resin has a Tg value of 35° C. or more, preferably 40 to150° C. and more preferably 50 to 130° C. A Tg value of less than 35° C.in the binding resin brings a possibility of rendering the formedantiloading coating so sticky as to lose antiloading function. Kinds ofthe binding resin include latexes such as natural rubber, butadienerubber, styrene-butadiene rubber, styrene-butadiene-acrylonitrilerubber, chloroprene rubber and methyl-butadiene rubber, and acrylic andvinyl acetate emulsions. Preferable binding resins arestyrene-butadiene-acrylonitrile rubber and styrene-butadiene rubber.

An antiloading agent composition is prepared by mixing an antiloadingagent, a binding resin and a solvent. With regard to components of theantiloading agent composition, conventionally known additives may bemixed thereinto in the quantities typically used, such as asurface-active agent, a plasticizer, an antistatic agent, a humidifyingagent, an antifoaming agent, a coloring matter, a pigment and a filler.Each of the components may also be mixed in a form of being previouslydispersed into a solvent in a proper quantity.

A binding resin is contained in the antiloading agent composition in thequantity occupying 5 to 50% of the formed antiloading coating on thebasis of solid content weight, preferably 10 to 40% and more preferably15 to 35%. A binding resin content of less than 5% in the antiloadingcoating decreases the proportion of the binding resin component soextremely as to deteriorate the retention of an antiloading agent on asurface of a coated abrasive material, while a binding resin content ofmore than 50% therein renders the proportion of the binding resincomponent more than the antiloading coating to deteriorate an originalfunction of the antiloading agent for preventing swarf from adhering.

An antiloading agent composition is applied on an outermost surface ofan abrasive material by methods such as brush coating, roll coating,flow coating, die coating and spray coating. The applied quantity mayproperly vary with the size and quantity of abrasive grains to be usedand the use of the abrasive material, generally being approximately 1 to75 g/m² as dried coating weight, preferably approximately 9 to 40 g/m².

Then, an abrasive material on which an antiloading agent composition isapplied is preferably heated and dried at temperature and timeappropriate for forming a selected binding resin into a film with cracksto form a reticulate fine structure on an entire surface of the coatingby the cracks. The heating conditions can be properly determined bythose skilled in the art.

For example, an abrasive material is heated at a temperature higher thanTg of a binding resin, preferably a temperature 1 to 60° C. higher thanTg of a binding resin and more preferably a temperature 10 to 40° C.higher than Tg of a binding resin. A heating temperature lower than Tgof a binding resin dries the binding resin with a granular stateretained not to be formed into a film or to be insufficiently formedinto a film, while a heating temperature more than 60° C. higher than Tgof a binding resin makes an antiloading agent composition into souniform film as to be incapable of obtaining a reticulate fine structureby the cracks.

The heating time is 0.5 to 30 minutes, preferably 1 to 15 minutes. Aheating time of less than 0.5 minute does not sufficiently volatilizeand dry a solvent to perform no antiloading function, while a heatingtime of more than 30 minutes results in the deterioration anddiscoloration of an antiloading agent composition and theuniformalization of a film.

The obtained antiloading coating is formed into a film by fusing theparticles of a binding resin and the appearance of the coating istransparent. That is, the antiloading coating obtained by a method ofthe present invention exhibits light transmission properties. Therelative transmittance thereof is 1% or more, preferably 2 to 50% andmore preferably 10 to 40%. A relative transmittance of less than 1% inthe antiloading coating determines that an antiloading agent compositionis not formed into a film, whereby the effect of the present inventionis not obtained.

Also, with regard to a reticulate fine structure formed on an entiresurface of the coating by the cracks, the longest diameter of thelargest one among reticulations is 1000 μm or less, preferably 1 to 700μm and more preferably 5 to 500 μm. A longest diameter of more than 1000μm in the largest reticulation deteriorates capability of dischargingswarf which is exhibited by peeling off of an antiloading agentcomposition having a fine structure with the cracks. A reticulate finestructure of the coating by the cracks varies also with the size ofabrasive particles. The dimensions of reticulations are determined byobserving with a microscope.

Incidentally, an abrasive material on which an antiloading agentcomposition is applied has been conventionally heated only attemperature and time sufficient for drying a selected solvent;consequently, a binding resin is retained in a granular state and notformed into a film, and the appearance of the coating is opaque. Thereason therefor is that it has been thought that the formation of theantiloading coating into a film drops the antiloading agent off anabrasive material surface with such difficulty as to deteriorate afunction of discharging swarf, and thus the heating has been restrictedto a minimum performance.

An abrasive material of the present invention having an antiloadingcoating on an outermost surface thereof can be used for abrading variousworkpieces, woody materials such as wood, fiberboards and particleboards, fiberglass, varnish, polyester coatings, stainless surfaces, carbody fillers, ceramics, glass, paints starting with latexes and oilpaints, primers including oily primers and aqueous primers, and metalscontaining aluminum, stainless steel and mild steel.

The present invention is further detailed by the following examples andis not limited thereto. “Part” and “%” in the examples are on the basisof weight unless otherwise specified.

EXAMPLES Example 1

The Production of an Antiloading Agent Composition

While stirring calcium stearate dispersion (a solid content of 55%),brand name of NOPCO 1097-AH, manufactured by San Nopco Co. Ltd., Japan,with a mixer, LABO-STIRRER MODEL LR-518, manufactured by YamatoScientific Co. Ltd., Japan, at a number of revolutions of 500 rpm,styrene-butadiene-acrylonitrile latex (an aqueous dispersion, solidcontent of 49%, Tg of 105° C.), brand name of NIPOL LX311 manufacturedby Zeon Corp., Japan, was charged thereinto and stirred at roomtemperature for 10 minutes. The mixture ratio thereof was adjusted sothat the solid content weight ratio of calcium stearate toacrylonitrile-butadiene rubber is 8/2.

The production of an abrasive material having an antiloading coating onan outermost surface thereof

A coated abrasive material “Uni” (P120 grade) manufactured by 3M Ltd.was prepared. The antiloading agent composition was applied on a surfaceof a size coat of this coated abrasive material by using a hand rubberroller. The applied quantity was 0.3 g with respect to an area of 4inches×6 inches as dry coating weight. The temperature of an oven wasset at 120° C. and then the abrasive material on which the antiloadingagent composition was applied was put thereinto and heated for 2.5minutes. Thereafter, the abrasive material was taken out and cooled.

A surface of the formed antiloading coating was observed under amagnification of 150 times by using an electron microscope. FIG. 1 is anelectron micrograph showing a surface of the antiloading coating of theabrasive material in Example 1. The antiloading coating is formed into afilm with cracks and a reticulate fine structure is confirmed. Therelative transmittance of the antiloading coating measures 35% by usinga spectrophotometer “U-4000” manufactured by Hitachi, Ltd., Japan. Thelongest diameter of the largest one among reticulations by the cracks isapproximately 200 μm.

Abrasion Test

The obtained coated abrasive material was stamped into a disk having adiameter of 125 mm for an evaluation sample. A putty “High Soft Super”manufactured by 3M Ltd. was applied to a steel panel substrate, and itwas dried and cured. The cured putty was abraded by using a doubleaction sander “3965” manufactured by 3M Ltd., under the conditions of anabrasion load of 5 kg, an abrasion time of 3 minutes and an abrasionnumber of 3 times. The abraded quantity was converted into 118% withrespect to 100%, which was the abraded quantity (weight) obtained byusing an abrasive disk in Comparative Example 1 produced on currentheating conditions.

Next, a surface of the antiloading coating after being used for abradingwas observed under a magnification of 150 times by using an electronmicroscope. FIG. 2 is an electron micrograph showing a surface of theantiloading coating of the abrasive material in Example 1 after beingused. A fine structure of the antiloading coating is crushed and anantiloading agent is effectively dropped off.

Example 2

An abrasive material having an antiloading coating on an outermostsurface thereof was obtained for performing the abrasion test in thesame manner as Example 1 except for modifying the preset temperature ofan oven into 110° C. The properties and test results of the antiloadingcoating are shown in Table 1. FIG. 3 is an electron micrograph showing asurface of the antiloading coating of the abrasive material in Example2. FIG. 4 is an electron micrograph showing a surface of the antiloadingcoating of the abrasive material in Example 2 after being used.

Comparative Example 1

An abrasive material having an antiloading coating on an outermostsurface thereof was obtained in the same manner as Example 1 except formodifying the preset temperature of an oven into 100° C. FIG. 5 is anelectron micrograph showing a surface of the antiloading coating of theabrasive material in Comparative Example 1. The antiloading coating isnot formed into a film and offers no appearance of transparency. Therelative transmittance of the antiloading coating measures 0% by using aspectrophotometer “U-4000” manufactured by Hitachi, Ltd. Reticulationsby the clear cracks are not formed.

The abrasion test was performed in the same manner as Example 1 exceptfor using the obtained coated abrasive material. The abraded quantity(weight) obtained herein was determined at 100%, which was a benchmarkof the abraded quantities obtained in other examples and anothercomparative example. FIG. 6 is an electron micrograph showing a surfaceof the antiloading coating of the abrasive material in ComparativeExample 1 after being used. Particles of an antiloading agent arepartially dropped off and the antiloading coating is not crushed.

Comparative Example 2

An abrasive material having an antiloading coating on an outermostsurface thereof was obtained for performing the abrasion test in thesame manner as Example 1 except for modifying the preset temperature ofan oven into 90° C. The properties and test results of the antiloadingcoating are shown in Table 1. FIG. 7 is an electron micrograph showing asurface of the antiloading coating of the abrasive material inComparative Example 2. FIG. 8 is an electron micrograph showing asurface of the antiloading coating of the abrasive material inComparative Example 2 after being used. TABLE 1 Comparative ComparativeExample 1 Example 2 Example 1 Example 2 Heating 120 110 100 90Temperature (° C.) Transmittance 35 2 0 0 (%) Longest About 200 About500 Not Not Diameter of Observed Observed Reticulations (μm) Abraded 118108 100 98 Quantity (%)

1. An abrasive material having an antiloading coating on an outermostsurface thereof, wherein the antiloading coating contains an antiloadingagent and a binding resin; the binding resin is formed into a film withcracks; and a reticulate fine structure is formed on an entire surfaceof the antiloading coating by the cracks.
 2. An abrasive materialaccording to claim 1, wherein a longest diameter of a largest one amongreticulations of said fine structure is 1000 μm or less.
 3. An abrasivematerial according to claim 1, wherein said binding resin has a glasstransition temperature of 35° C. or more.
 4. An abrasive materialaccording to claim 1, wherein said binding resin is formed into a filmby drying particulate resin.
 5. An abrasive material according to claim4, wherein said particulate resin is an aqueous latex or an aqueousresin emulsion.